The present invention relates to a crash detector of the type which at strong retardation gives an indication that an accident, for instance a crash has just started and which thereby releases a safety means intended to reduce the effect of said crash. Detectors of this kind can be used in many different fields, and a fertile field of use is in motor vehicles, in which the crash detector at retardation over a predetermined limit can for instance release a means for tightening safety belts or car belts, provide an inflation of gas-filled damp cushions, release a fire extinguish means, start an alarm signal etc.
Crash detectors are previously known which comprise an inertia body, which is mounted in a cylinder or similar casing and which in the normal position is maintained in a position spaced from the said releaser means for instance by means of a spring or any other retaining means which in case of strong retardation brakes and releases the inertia body to allow said body to move towards the releaser means. The said crash detectors are disadvantageous in that it is very difficult to calculate the holder force for the spring or the retainer means so that unintentional release of the detector is prevented for instance at strong braking, unevenesses in the road or such small crashes which may occur when parking the vehicle etc. If on the other hand the holder force is too strong there is a risk that the crash damping means will never be released.
Some other types of crash detectors which likewise comprise an inertia body which is kept in a restored position by a spring is disadvantageous in that the holder spring must be very strong to eliminate the risk for release in case of strong braking, unevenesses in the road or when parking crashes occur, and this may have as an effect that the release of the safety means or crash damping means follows too late.